Method for forming active area and method for forming semiconductor structure

Abstract

A method for forming the active area includes the following operations. A semiconductor substrate is provided. A first mask layer and a second mask layer are sequentially formed on a surface of the semiconductor substrate, in which the second mask layer has an initial pattern for forming the active area. A sacrificial layer covering the second mask layer is formed. The sacrificial layer and a portion of the second mask layer are removed to form a third mask layer with a preset thickness, in which the preset thickness is less than an initial thickness of the second mask layer. The active area is formed through the third mask layer and the first mask layer.

What is claimed is: 
     
       1. A method for forming an active area, comprising:
 providing a semiconductor substrate; 
 sequentially forming a first mask layer and a second mask layer on a surface of the semiconductor substrate, wherein the second mask layer has an initial pattern for forming the active area; 
 forming a sacrificial layer covering the second mask layer; 
 removing the sacrificial layer and a portion of the second mask layer to form a third mask layer with a preset thickness, wherein the preset thickness is less than an initial thickness of the second mask layer; and 
 forming the active area through the third mask layer and the first mask layer; 
 wherein removing the sacrificial layer and the portion of the second mask layer to form the third mask layer with the preset thickness comprises: 
 thinning the sacrificial layer and the second mask layer and removing the portion of the second mask layer to form the third mask layer with the preset thickness and the sacrificial layer with the preset thickness, wherein the third mask layer has the initial pattern; and 
 removing the sacrificial layer with the preset thickness; 
 wherein 
 the initial pattern in the third mask layer exposes a portion of the first mask layer; and 
 wherein forming the active area through the third mask layer and the first mask layer comprises: 
 forming a spacer material layer on a surface of the portion of the first mask layer exposed by the initial pattern in the third mask layer and a surface of the third mask layer; 
 removing a portion of the spacer material layer and a portion of the third mask layer to form a fourth mask layer; and 
 forming the active area through the fourth mask layer and the first mask layer. 
 
     
     
       2. The method according to  claim 1 , wherein
 the second mask layer comprises a first hard mask layer, a second hard mask layer and an anti-reflection layer sequentially stacked on one another from bottom to top; and 
 wherein thinning the sacrificial layer and the second mask layer and removing the portion of the second mask layer to form the third mask layer with the preset thickness comprises: 
 thinning the sacrificial layer, the anti-reflection layer and the second hard mask layer, and remaining a portion of the second hard mask layer to form the third mask layer. 
 
     
     
       3. The method according to  claim 1 , wherein
 forming the second mask layer comprises the following operations: 
 sequentially forming a second initial mask layer and a patterned photoresist layer on a surface of the first mask layer, wherein the patterned photoresist layer has the initial pattern; and 
 etching the second initial mask layer through the patterned photoresist layer to obtain the second mask layer with the initial pattern. 
 
     
     
       4. The method according to  claim 3 , further comprising:
 removing the patterned photoresist layer after forming the second mask layer. 
 
     
     
       5. The method according to  claim 2 , wherein
 the initial pattern in the second mask layer exposes a portion of the first mask layer; and 
 wherein forming the sacrificial layer covering the second mask layer comprises: 
 depositing a sacrificial material on a surface of the portion of the first mask layer exposed by the initial pattern in the second mask layer and a surface of the second mask layer to form the sacrificial layer. 
 
     
     
       6. The method according to  claim 5 , wherein
 an etching selectivity ratio of the sacrificial material to the first mask layer is greater than an etching selectivity ratio of the first hard mask layer to the first mask layer, and the etching selectivity ratio of the sacrificial material to the first mask layer is greater than an etching selectivity ratio of the second hard mask layer to the first mask layer. 
 
     
     
       7. The method according to  claim 1 , wherein
 the spacer material layer comprises a first spacer material layer and a second spacer material layer; and 
 wherein forming the spacer material layer on the surface of the portion of the first mask layer exposed by the initial pattern in the third mask layer and the surface of the third mask layer comprises: 
 depositing a first spacer material on a top portion and sidewalls of the third mask layer and the surface of the portion of the first mask layer exposed by the initial pattern in the third mask layer to form the first spacer material layer; and 
 depositing a second spacer material on a surface of the first spacer material layer to form the second spacer material layer. 
 
     
     
       8. The method according to  claim 7 , wherein
 the third mask layer comprises the first hard mask layer and the portion of the second hard mask layer; and 
 wherein removing the portion of the spacer material layer and the portion of the third mask layer to form the fourth mask layer comprises: 
 planarizing the spacer material layer until a top surface of the second hard mask layer is exposed, wherein a remaining portion of the first spacer material layer has a plurality of U-shaped structures, each U-shaped structure being formed by two vertical spacers and a horizontal spacer; 
 removing the vertical spacers in the remaining portion of the first spacer material layer; and 
 removing the second hard mask layer and a remaining portion of the second spacer material layer to form the fourth mask layer. 
 
     
     
       9. The method according to  claim 8 , wherein
 the fourth mask layer has a preset pattern, and a pattern density of the preset pattern is greater than a pattern density of the initial pattern. 
 
     
     
       10. The method according to  claim 1 , wherein
 forming the active area through the fourth mask layer and the first mask layer comprises: 
 etching the first mask layer through the fourth mask layer to transfer the preset pattern into the first mask layer to obtain a patterned first mask layer; and 
 etching the semiconductor substrate through the patterned first mask layer to form the active area. 
 
     
     
       11. The method according to  claim 10 , further comprising:
 removing the fourth mask layer after forming the patterned first mask layer. 
 
     
     
       12. The method according to  claim 11 , further comprising:
 removing the patterned first mask layer after forming the active area. 
 
     
     
       13. A method for forming a semiconductor structure, comprising:
 providing a semiconductor substrate; 
 forming an active area on the semiconductor substrate; 
 forming word lines, wherein the word lines intersect with the active area in a word line extension direction; and 
 forming bit lines, wherein the bit lines intersect with the active area in a bit line extension direction, 
 wherein forming the active area on the semiconductor substrate comprises: 
 providing the semiconductor substrate; 
 sequentially forming a first mask layer and a second mask layer on a surface of the semiconductor substrate, wherein the second mask layer has an initial pattern for forming the active area; 
 forming a sacrificial layer covering the second mask layer; 
 removing the sacrificial layer and a portion of the second mask layer to form a third mask layer with a preset thickness, wherein the preset thickness is less than an initial thickness of the second mask layer; and 
 forming the active area through the third mask layer and the first mask layer; 
 wherein removing the sacrificial layer and the portion of the second mask layer to form the third mask layer with the preset thickness comprises: 
 thinning the sacrificial layer and the second mask layer and removing the portion of the second mask layer to form the third mask layer with the preset thickness and the sacrificial layer with the preset thickness, wherein the third mask layer has the initial pattern; and 
 removing the sacrificial layer with the preset thickness; 
 wherein 
 the initial pattern in the third mask layer exposes a portion of the first mask layer; and 
 wherein forming the active area through the third mask layer and the first mask layer comprises: 
 forming a spacer material layer on a surface of the portion of the first mask layer exposed by the initial pattern in the third mask layer and a surface of the third mask layer; 
 removing a portion of the spacer material layer and a portion of the third mask layer to form a fourth mask layer; and 
 forming the active area through the fourth mask layer and the first mask layer.